Recent reports suggest that unfractionated heparin may be a useful adjunct in the treatment of inflammatory bowel disease (IBD). We report the successful use of subcutaneous unfractionated heparin to treat a moderate-to-severe flare of Crohn's disease during pregnancy, which was refractory to standard therapy. The patient received 10,000 units of unfractionated heparin subcutaneously twice a day after her Crohn's colitis failed to come under remission with intravenous corticosteroids. Heparin was continued throughout her pregnancy. Following initiation of adjunctive heparin therapy, the patient experienced a rapid clinical response, was able to discontinue intravenous steroids, discharge from the hospital, and ultimately deliver a healthy term newborn. Although there is extensive obstetric experience with heparin in the treatment of thrombosis associated with pregnancy, there is limited information regarding its use in IBD patients during pregnancy. Because heparin has an established track record in maternal-fetal medicine, this agent may be considered in women who suffer an inflammatory flare of IBD during pregnancy who have not responded to standard treatment.